The inventions referred to above relate generally to a liquid dispenser and, more particularly, to an automatic liquid dispenser useful in a variety of applications in which a constant volume of liquid needs to be dispensed at periodic time intervals. The present invention relates generally to flow controls which effect fluidic system response and, more specifically, to a process for making flow restrictors having predetermined flow rate versus pressure drop characteristics. In one application, the flow restrictors made according to the present invention find advantageous use with my automatic liquid dispensers referred to above.
Dispensing liquids on a periodic basis is a common task around the home, workplace, or laboratory. Typical applications that require liquid to be dispensed in a controlled fashion include plant watering/feeding, fertilizing, air freshening, drain cleaning, toilet bowl cleaning, pet watering, medicating, lubricating, humidifying and fumigating.
Devices for restricting flow, such as orifices and capillary tubes, are well known. To achieve high resistances to flow, however (such as required in the microflow dispensing apparatuses of my inventions referred to above, and specifically described below), extremely small orifices or extremely long capillary tubes are required. These types of flow restrictors can also be expensive to manufacture, and can be easily clogged.
I have previously determined that certain materials, such as compressed fibers, can be used as flow restriction devices where very high flow resistance is necessary. However, flow restrictors, particularly those used for dispensing at microflow rates, typically must be set very accurately, since the performance of the individual dispenser can otherwise vary widely. Accordingly, the high volume yet economical production of precision-set flow restrictors is necessary.
A flow restrictor can be fabricated by pulling a fibrous cord material through a sleeve having a diameter less than that of the cord, thereby compressing the cord fibers. However, manufacturing variations in cord tension, sleeve and cord diameters, and cord density can cause wide variations in flow restrictor performance. Thus, while the flow restrictor disclosed in U.S. Ser. No. 08/231,742 has met with some success, some disadvantages associated with consistent performance still exist.
It has been found that if certain materials, such as a fibrous cord, are compressed within a loose-fitting metal sleeve, some improvement in the fabrication of consistent flow restrictors is achieved. However, the cord density and sleeve dimensional tolerances were still found to result in the fabrication of flow restrictors with disadvantages concerning consistent performance.
The present invention concerns an improved flow control device to overcome certain disadvantages associated with flow restrictor performance.